1. Field of the Invention
The present invention relates to an information recording medium having a track, which is subjected to wobbling, and an information reading apparatus for reading information of the track.
2. Description of the Related Art
Currently, an optical disk typified by a CD and a DVD has been put into practice. In addition to a CD-DA (CD-Digital Audio) and so on, which is a recording medium only for reproducing, in recent years, CD-R (CD-Recordable) for one-time recording digital data and CD-RW (CD-ReWritable) for rewriting digital data for two or more times and so on also have been put into practice.
In recording and reproduction of an optical disk, the optical disk needs to be rotated at a predetermined speed. In the case of a recording medium only for play, a predetermined rotation speed can be obtained by synchronizing a rotation speed to a reproducing frequency of digital data during reproduction. Meanwhile, in the case of a recordable recording medium such as CD-R and CD-RW, in an initial state, digital data is not recorded in a track, so that the same method cannot be used for controlling a rotation speed. Thus, in a recordable recording medium, a track (groove track) is subjected to wobbling according to a wobble signal obtained by performing FM modulation on a wobble reference signal, which has a predetermined fundamental frequency, based on address information, a rotation speed of the optical disk is controlled in response to the wobble reference signal extracted from a wobble signal read from the track, and the address of the track is identified by demodulating the wobble signal.
However, crosstalk and so on enters a wobble signal. The crosstalk is caused by wobble from an adjacent track or by a recording mark formed on a track which is subjected to wobbling a wobble signal. Hence, the wobble signal has a degraded CN (Carrier to Noise ratio), a problem occurs on reading of address information recorded by FM modulation and so on, and the reference signal extracted from the wobble signal becomes inaccurate. Further, in the case of a multilayer disk as well, the same problem results from crosstalk of a wobble signal between layers. Hence, it is difficult to accurately perform writing in the multilayer disk.
For example, when a track pitch is smaller, a beam extends substantially to an adjacent groove and is affected by a phase of wobble of the adjacent track. Besides, since a phase changes complicatedly between adjacent grooves, a value of a reading signal based on reflected light of the beam is largely changed by the influence of the adjacent track.
As described above, in the conventional method, when the track is affected by noise and crosstalk, it is difficult to detect a signal with accuracy.